1. Field of the Invention
The present invention relates to the field of integrated circuit packaging.
2. Prior Art
In certain applications it is desirable to package multiple circuits or multiple circuit functions in a single integrated circuit package. One such application is in power regulation wherein a switching regulator controller is desired to be packaged with the power transistors controlled by the controller. Such packaging has been accomplished in the prior art using various techniques. In particular, two separate integrated circuits can be packaged together side by side on a substrate as a multi-chip module, though that is expensive, not of high performance and wastes printed circuit board area. A second approach is to simply stack the two integrated circuits, though that too is expensive as electrical connections from the upper chip must be coupled through the bottom chip, both for connection to the circuit thereon and for connection to the printed circuit board.
Finally, the power transistors and the controller may be fabricated as a single monolithic circuit. This, of course, has the advantage of providing a truly monolithic device, though has certain disadvantages leading to substantially higher costs, which disadvantages can also reduce the performance, particularly of the power transistors. In particular, the controller chip area is normally much smaller than the MOSFET chip area and of course is a much more complex circuit, requiring many more processing steps for the fabrication thereof. The power transistors, on the other hand, are simple structures requiring far fewer processing steps than the controllers. Consequently, when such a monolithic circuit is fabricated the full controller processing is required, though the number of actual controllers fabricated per wafer is far below the number of controllers that would be obtained by the same process by fabricating the controller separately. Further, the power transistors, while not requiring it, are subjected to all the additional steps which can degrade the performance of the power transistors. Accordingly this monolithic solution is particularly expensive.